I bought both medium and hard strings, and you can definitely feel the difference while playing. It’s not that one is better than the other—it just depends on the sound you’re looking for. I use the hard strings for fiddle-style playing (bluegrass and similar genres) and the medium strings for classical music. Both sets are for my electric violin, which I use on my Yamaha SV130.
At first, the strings went out of tune quite quickly, but after 2–3 weeks of regular playing, they settled in and became more stable. I would recommend the hard strings for fiddle playing rather than classical, as they suit that style better.